Fig. 1

MRI of a subject’s lumbar spine and target muscle measurements. (A) Sagittal view of the lumbar spine, with the yellow line indicating the location of the measured cross-sectional MRI; (B) Cross-sectional area of the psoas major (PM), quadratus lumborum (QL), multifidus (MF), and erector spinae (ES) at the L1/2 segment; (C) Functional cross-sectional area of the PM, QL, MF and ES at the L1/2 segment. LPM left psoas major, LQL left quadratus lumborum, LMF left multifidus, LES left erector spinae, RPM right psoas major, RQL right quadratus lumborum, RMF right multifidus, RES right erector spinae.